Conventionally, water-in-oil type emulsion compositions having an oil phase as an external phase and a water phase as an internal phase are a type of formulation that is suitable for use as formulations for external application to the skin due to their ability to effectively spread oil-soluble active ingredients, such as emollient oils, oil-soluble medicinal agents and UV absorbing agents over the skin, and are widely used in the cosmetic field, such as in skin care creams, milky lotions, and hair care creams.
However, water-in-oil type emulsion cosmetic compositions are often stabilized by gelling the oils constituting the external phase so as to immobilize water droplets and lower the collision frequency of the particles, thus requiring the viscosity to be raised. For this reason, it was considered to be difficult to achieve both low viscosity and stability in water-in-oil type emulsion cosmetic compositions, and it was difficult to simultaneously improve the stability over time and the spreadability and sensation of use at the time of application.
Various attempts have been made until now toward achieving water-in-oil type emulsion cosmetic compositions with low viscosity and stability. For example, Patent Document 1 proposes the use of a mixed powder combining highly oil-absorbent powders which are powders of different particle sizes (in other words, a powder mixture of a spherical organopolysiloxane elastomer powder and a hydrophobic silica powder) at a specific weight ratio, an oil part comprising 30 wt % or more of a silicone oil, and an organically modified clay mineral as an auxiliary emulsifier. Additionally, Patent Document 2 proposes the use of a specific hydrophobized silica as an emulsion stabilizer, and the use of a specific silicone surfactant as an emulsifier to improve the stability over time of the emulsion state, the feel and the texture.
However, in conventional low-viscosity water-in-oil type emulsion cosmetic compositions as mentioned above, there is a tendency for the amount of surfactant distributed to the oil phase to increase, making emulsification difficult, and resulting in a substantial loss of stability. Additionally, while polar oils have the action of stably dissolving various medicinal agents such as UV absorbing agents that have low solubility in non-polar oils, there are restrictions on the medicinal agents and the like that can be blended in low-viscosity water-in-oil type emulsion cosmetic compositions that cannot easily be provided with a high polar oil content. As a result, in order to obtain high SPF effects, for example, they must be made in a two-layer separated type in which the oil phase and the water phase are separated during storage, thus being inferior in terms of handling and the like.